TY - JOUR

T1 - Hot organic molecules toward a young low-mass star

T2 - A look at inner disk chemistry

AU - Lahuis, F.

AU - Van Dishoeck, E. F.

AU - Boogert, A. C.A.

AU - Pontoppidan, K. M.

AU - Blake, Geoffrey A.

AU - Dullemond, C. P.

AU - Evans, N. J.

AU - Hogerheijde, Michiel R.

AU - Jørgensen, J. K.

AU - Kessler-Silacci, J. E.

AU - Knez, C.

PY - 2006/1/10

Y1 - 2006/1/10

N2 - Spitzer Space Telescope spectra of the low-mass young stellar object (YSO) IRS 46 (Lbol ≈ 0.6 L⊙) in Ophiuchus reveal strong vibration-rotation absorption bands of gaseous C2H2, HCN, and CO2. This is the only source out of a sample of ∼ 100 YSOs that shows these features, and this is the first time that they are seen in the spectrum of a solar-mass YSO. Analysis of the Spitzer data combined with Keck L- and M-band spectra reveals excitation temperatures of ≥350 K and abundances of 10-6 to 10-5 with respect to H2, orders of magnitude higher than those found in cold clouds. In spite of this high abundance, the HCN J = 4-3 line is barely detected with the James Clerk Maxwell Telescope (JCMT), indicating a source diameter less than 13 AU. The (sub)millimeter continuum emission and the absence of scattered light in near-infrared images limit the mass and temperature of any remnant collapsing envelope to less than 0.01 M⊙ and 100 K, respectively. This excludes a hot-core-type region as found in high-mass YSOs. The most plausible origin of this hot gas rich in organic molecules is in the inner (<6 AU radius) region of the disk around IRS 46, either the disk itself or a disk wind. A nearly edgeon two-dimensional disk model fits the spectral energy distribution (SED) and gives a column of dense warm gas along the line of sight that is consistent with the absorption data. These data illustrate the unique potential of high-resolution infrared spectroscopy to probe the organic chemistry, gas temperatures, and gas kinematics in the planet-forming zones close to a young star.

AB - Spitzer Space Telescope spectra of the low-mass young stellar object (YSO) IRS 46 (Lbol ≈ 0.6 L⊙) in Ophiuchus reveal strong vibration-rotation absorption bands of gaseous C2H2, HCN, and CO2. This is the only source out of a sample of ∼ 100 YSOs that shows these features, and this is the first time that they are seen in the spectrum of a solar-mass YSO. Analysis of the Spitzer data combined with Keck L- and M-band spectra reveals excitation temperatures of ≥350 K and abundances of 10-6 to 10-5 with respect to H2, orders of magnitude higher than those found in cold clouds. In spite of this high abundance, the HCN J = 4-3 line is barely detected with the James Clerk Maxwell Telescope (JCMT), indicating a source diameter less than 13 AU. The (sub)millimeter continuum emission and the absence of scattered light in near-infrared images limit the mass and temperature of any remnant collapsing envelope to less than 0.01 M⊙ and 100 K, respectively. This excludes a hot-core-type region as found in high-mass YSOs. The most plausible origin of this hot gas rich in organic molecules is in the inner (<6 AU radius) region of the disk around IRS 46, either the disk itself or a disk wind. A nearly edgeon two-dimensional disk model fits the spectral energy distribution (SED) and gives a column of dense warm gas along the line of sight that is consistent with the absorption data. These data illustrate the unique potential of high-resolution infrared spectroscopy to probe the organic chemistry, gas temperatures, and gas kinematics in the planet-forming zones close to a young star.

KW - Infrared: ISM

KW - ISM: individual (IRS 46)

KW - ISM: jets and outflows

KW - ISM: molecules

KW - Planetary systems: protoplanetary disks

KW - Stars: formation

UR - http://www.scopus.com/inward/record.url?scp=32044466218&partnerID=8YFLogxK

U2 - 10.1086/500084

DO - 10.1086/500084

M3 - Journal article

AN - SCOPUS:32044466218

VL - 636

SP - L145-L148

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 2 II

ER -